I suspect the tip temperature is related to the flux more than the solder itself. When you buy flux cored solder wire, the flux contained in the wire is the most important part of the specification. It can be rosin, or RMA, or RA, or water soluble, or non-rosin, or others, and the percent flux can vary.
You didn't mention what kind of flux your solder has? I would guess if the tip temperature is too high it might prevent the flux operating properly.